Gelled aqueous explosive composition having hydrogen cyanamide as antifreezing agent



3,397,095 GELLED AQUEOUS EXPLOSIVE COMPOSITION HAVING HYDROGEN CYANAMIDEAS ANTI- FREEZING AGENT John Patrick Merryweather and John AubreyMcLean,

Niagara Falls, Ontario, and Trevor David Field, Chippawa, Ontario,Canada, assignors to American Cyanamid Company, Stamford, *Conn., acorporation of Maine No Drawing. Filed Dec. 14, 1966, Ser. No. 601,563 9Claims. (Cl. 149-39) ABSTRACT OF THE DISCLOSURE Anti-freeze propertiesare provided in water-base, ammonium nitrate explosive gel compositionsby the incorporation therein of a small amount of hydrogen cyanamide andespecially by the incorporation of small amounts of both hydrogencyanamide and urea.

This invention relates to new and improved aqueous gel explosivecompositions. More particularly, it relates to gelled ammonium nitrateexplosive compositions having outstanding anti-freeze properties.

Aqueous slurry-type explosive compositions comprising ammonium nitrateand an explosive sensitizer, such as trinitrotoluene, smokeless powder,dinitrotoluene, etc., have attained substantial commercial acceptance.It has been recognized, however, that these compositions, While highlyuseful, possess certain drawbacks. Thus, they tend to separate intolayers, each containing different proportions of the various components.Because of this, these compositions are oftentimes not only difficult tohandle, but their non-uniform consistency adversely affects theirexplosive characteristics and consequently their reliability in use.

Recently, it has been shown that the separation problem and difficultiesattendant therewith can be counteracted to a substantial extent by theincorporation in the slurry compositions of various gel-formingmaterials which increase the viscosity of the compositions and therebyreduce the settling tendency of the solid components. Thus, the gelledcompositions generally exhibit improved, uniform consistency and at thesame time sufficient fluidity to permit easy handling and pouring.

It has been further recognized in the art with respect to explosive gelcompositions that their stability is enhanced by the incorporationtherein, along with the gelling agent, of a small amount of across-linking agent in the form of a polyvalent metal salt. Salts ofaluminum, chromium, iron, tin, and the like have been used. Theparticular anion of the salt does not appear to be critical. Sulfateshave been commonly used, particularly, aluminum sulfate. Nitrates andchlorides have also proved effective, particularly, chromium nitrate.

While the explosive gel compositions represent a substantial advanceover the non-gelled, slurry-type compositions, they still possess atroublesome defect. Thus, the gels tend to harden considerably onstanding, rather than remaining uniformly soft and pourable,particularly when exposed to temperatures in the order of F. or below. Aprime characteristic and advantage of the explosive gels is, of course,their pourability, by virtue of which they are readily and elficientlyloaded into bore-holes. In the hardened or semi-hardened state, thisadvantage is, of course, greatly reduced or lost entirely. Accordingly,it is evident that the hardening of the gels at the aforesaidtemperatures, which are not uncommon in northern mining operationsduring the winter, constitutes 'a serious drawback to their use.

Although the gels in the hardened or semi-hardened nited States Patent 0"ice state are sometimes referred to as being frozen, this is somewhatof a misnomer since the hardening of the gel is not the result offreezing in the conventional sense, but rather of the salting out ofcrystals from the saturated ammonium nitrate and/or sodium nitratesolution which is a component of the gel compositions. Thus, thesolidifying effect can occur at temperatures well above freezing,although it becomes more pronounced as the temperature to which thecompositions are exposed becomes lower. On this basis, a gel compositionwhich exhibits pronounced hardening tendencies particularly when exposedto relatively low temperatures is said to have poor anti-freezeproperties.

More recently, it has been shown in the prior art that the non-hardeningor anti-freeze properties of the gelled explosive compositions can besubstantially improved by the incorporation therein, in minor amounts,of certain compounds generally referred to as fiuidizing agents. Avariety of such fiuidizing agents, including, inter alia, certainalcohols, organic acids, amines and amides, are shown for example in US.Patent No. 3,190,777. Also, the use of urea is shown in Canadian PatentNo. 712,981.

While all of the fiuidizing agents of the prior art improve ttheanti-freeze properties of the gelled explosive compositions, the extentof the improvement is generally limited. Thus, with few exceptions, thelowest temperature at which the compositions employing them willconsistently retain the desired fluidity is about 0 C. A limiting factorwith respect to the use of the known fiuidizing agents, especially forprotection at sub-zero temperatures, is that the amounts thereofrequired are such as to adversely affect either the sensitivity orstrength of the explosive compositions. The protection afforded by theprior art anti-freeze agents where the explosives are exposed tosub-zero temperatures has therefore, not been wholly satisfactory. Theart has, therefore, sought fiuidizing agents capable of maintaining thegels in fluid or semifluid condition at sub-zero temperatures and whichat the same time can be used in amounts sufficiently low as not todetract from the explosive properties of the explosive composition. Itis an object of this invention to provide such a fiuidizing agent. Otherand further objects will become apparent from the following descriptionof the invention.

In accordance with the present invention it has been found that byemploying hydrogen cyanamide as a fiuidizing agent in the gelcompositions, the gels consistently retain the desired fluidity attemperatures down to 2() F. with no detraction from their sensitivity orstrength. It has further been found that by replacing part of thehydrogen cyanamide with urea still further improved antifreezeproperties are provided in the gels.

As is well known, hydrogen cyanamid-e, H NCN, is a normally unstablecompound which tends to decompose rather rapidly into dicyanamide andurea. However, it is marketed by American Cyanamid Company in the formof a buffered 50% aqueous solution designated as either AC50 orCyanamide SO. In this form the hydrogen cyanamide exhibits excellentstability for a period of at least three months, provided only that thesolution is stored at low temperature, i.e., below about 50 F. andpreferably below 30 F. It is this solution which is utilized to supplythe hydrogen cyanamide fiuidizing agent in the compositions of theinvention. It is referred to hereinafter as hydrogen cyanamide solutionor AC-50 As is well known, water-based explosive gels ordinarily containas essential components (a) ammonium nitrate either alone or incombination with a metal nitrate, such as sodium nitrate, (b) asensitizer or sensitizing fuel, (c) water, and (d) a suitable gellingagent. The sensitizer (or sensitizing fuel) may be of the self-explosivetype,

such as smokeless powder, TNT, pentaerythritol tetranitrate (PETN),cyclotrimethylenetrinitramine (RDX) andcyclotetramethylenetetranitramine (HMX) as well as mixtures thereof,such as pentolite (PETN/TNT), Composition B (RDX/TNT) and other knownequivalents. The self-explosive sensitizer may be in any of theconventional forms, i.e., flake, pellets or crystals. Also, thesensitizer may be comprised of any of the known metallic fuels, such asaluminium, magnesium, iron or alloys thereof, or ferrosilicon orferrophosphorus in finely divided form, which metallic fuels though notself-explosive provide sensitizing action when combined with anoxidizing salt, such as ammonium nitrate. Also, the sensitizer may be acarbonaceous material, such as charcoal, or a non-high explosive oil,such as dinitrotoluene or fuel oil.

The gelling agent may be any of the materials known to the art for thispurpose, e.g., synthetic gelling agents, such as cross-linked acrylamidepolymers of high molecular weight, various natural gelling agents, suchas gum arabic, guar, starches, dextrins, cellulose derivatives, gelatin,etc. A particularly successful material however, is guar gum and it ispreferred for the compositions of the present invention.

Various procedures used for the manufacture of aqueous explosive gelshave been shown in the prior art. A common practice is so-called in bowlmixing whereby all of the ammonium nitrate, sodium nitrate, sensitizerand gelling agent are added as dry ingredients to a mixing bowl,followed by the addition of hot water with continued mixing in order todisperse and dissolve the gelling agent. If necessary, a cross-linkingagent is then added with further mixing until the gelled product isobtained. Another well-known technique involves preparation of asaturated solution comprising a portion of the ammonium nitratecomponent and all of the sodium nitrate component. This stock solutionis then combined with the remainder of the ammonium nitrate component,the sensitizer, the gelling agent and the cross-linking agent. However,this order of mixing is not always used. Thus, in preparing thecompositions of the present invention using guar gum as the gellingagent, it has been found preferable not to include the sodium nitratecomponent in the ammonium nitrate stock solution, but to add it afterthe gelling agent has been added, since it tends to inhibit the initialgellation of the guar gum. For the same reason 4:

when the in bowl mixing procedure is used the sodium nitrate should beadded after the guar gum.

Other variations in manufacturing technique will be apparent to thoseskilled in the art. It will be appreciated, therefore, that the presentinvention does not reside in, nor is it limited in any way by, themanufacturing procedure used to prepare the improved compositionsthereof.

A full understanding of the invention will be had by reference to thefollowing specific examples and tests.

EXAMPLES 1-24 Parts Weight percent Ammonium Nitrate 30 62. 5O Urea. 3 6.25 Water 15 31. 25

The other ingredients of the compositions, including any additionalsolid ammonium nitrate to satisfy formulation requirements, were thenadded to the stock solution in a ribbon blender at 110-l20 F. Sodiumnitrate was omitted from the stock solution and added to the blenderlast because it was found to inhibit the initial gelling of the guar gumgelling agent.

A typical procedure was that of Example 19, as follows. To 5 pounds ofammonium nitrate and 20 pounds of flake TNT in the blender, 48 pounds ofstock solution were added and the whole mixed for one minute. Two poundsof hydrogen cyanamide solution were then added and mixed in for /2minute after which a premix of 14 pounds of aluminium powder and 1 poundof guar gum were added. The mixing was then continued until hydrationhad advanced to a thick enough consistency to suspend the solids, i.e.,about 4 minutes. Finally, 10 pounds of sodium nitrate were added andmixing continued until the mix was homogeneous, about one minute.

In the case of those compositions which did not contain hydrogencyanamide solution and/or aluminium the procedure was similar, exceptthat the addition of these ingredients was omitted.

The compositions of Examples l-4 and 9-16 which did not contain ureawere prepared by an in bowl mixing procedure. The preparation of Example16 which is typical was as follows. To 30 pounds of ammonium nitrate and25 pounds of TNT prills in the blender there was added 16 pounds of hot(-180" F.) water and the whole mixed to dissolve most of the ammoniumnitrate (about 2-3 minutes). Four pounds of hydrogen cyanamide solutionwere then added and the whole again mixed for half a minute. A premix of14 pounds of aluminium powder and 1 pound of guar gum were then addedand the mixing continued until hydration had advanced to a thick enoughconsistency to suspend the solids (about 4 minutes). Finally, 10 poundsof sodium nitrate was added and the mixing continued until the wholecomposition was homogeneous (about 1 minute).

Here again, in the case of those compositions which did not containhydrogen cyanamide solution and/or aluminium, the procedure was similarto that of Example 16, except that the addition of these ingredients wasomitted.

Upon completion of preparation each of the 24 compositions wasmagazine-stored for 24 hours to permit cooling and complete hydration ofthe guar gum before being subjected to cold storage tests. The averagetemperature of the gels at the end of this period was 60 F.

Anti-freeze tests Samples of each of the 24 compositions were extrudedinto plastic bags of uniform size and placed in low temperature storageat controlled temperatures of 20 F., 0 F., -10 F., -15 F., and 20 F. forseven days, after which they were examined and rated for theiranti-freeze properties as follows.

Poor: Gels which were hard and did not yield under hand pressure orwhich yielded with fracture.

Fair: Gels which were firm but which deformed under hand pressure.

Good: Gels which were soft and pliable.

Very good: Gels which were very soft and very pliable.

The pertinent data with respect to the 24 compositions and the testresults are summarized in Table I, in which the proportions ofcomponents are given in weight percents.

As will be seen from the table, control Examples 1-4 which contained nofluidizing agent (i.e., either AC-50 or urea) rated poor (P) at 20 F.

Also, of Examples 5-8, which contained 3% urea, three, i.e., Examples5-7, rated poor (P) at 0 F. while Example 8 rated fair (F) at 0 C. andpoor at l0 F.

Further, it is seen that Examples 9-12 which contained 2% AC-50 showedeither good (G) or very gOOd (VG) anti-freeze properties at -10 F. withthese properties declining at -15 F. and being lost entirely at 20 F. inthe case of Examples 9 and 10.

TABLE I Ammonium Sodium TNT Type Guar Anti-Freeze Rating F. Ex. No.Nitrate Nitrate Urea AC-50" Aluminum Gum Water Flake Prill 20 15 10 +2049 25 1 44 10 30 1 40 10 1 35 10 1 46 10 25 1 41 10 w 1 37 10 20 1 32 1025 1 46 10 2 o 25 1 P 43 10 2 28 1 P 37 10 2 20 1 F 32 10 2 25 1 F 44 104 25 1 F 41 10 4 28 1 F 10 4 20 1 G 30 10 4 14 25 1 G 44 10 3 2 25 1 F39 10 3 2 30 1 V G 35 10 3 2 14 20 1 G 30 7 3 2 14 28 1 G 42 10 3 4 25 1VG 37 10 3 4 30 1 V G 33 10 3 4 14 20 1 VG 30 5 3 4 14 28 1 VG Stillfurther, it is seen that Examples 13-16 which contained 4% of AC-50 hadimproved ratings over Examples 9-12, with Examples 13 and 14 being fair(F) and Examples 15 and 16 being good (G) at -20 F.

It is seen further that Examples 17-20, which contained a combination of3% urea and 2% AC-50 exhibited anti-freeze properties at least equal toExamples 13-16, with an improvement in Example 18 to a rating of verygood (VG) at -20 F.

Finally, it will be seen that Examples 21 to 24, which contained 3% ureaand 4% AC-50, all rated very good (VG) at 20 F.

It is evident, therefore, that hydrogen cyanamide is an effectiveanti-freeze agent for gelled water-based explosive compositions and thatthe combination of hydrogen cyanamide and urea provides outstandinganti-freeze properties in these compositions.

The compositions of the invention were also subjected to initiationpropagation and detonation tests at temperature ranging from 70 F. downto 20 F. without indication of any adverse effect.

As previously indicated, the anti-freeze improvements of this inventioncan be applied to water-based explosive gel compositions in general, theexamples given herein being merely illustrative of such compositions.Thus, such compositions generally may contain from about 15-50% byweight of ammonium nitrate, about 5-25% by weight of sodium nitrate,about 5-40% by weight of sensitizer (or fuel), from about 0.5-2% byweight of gelling agent and from about 5-25% by weight water. Also,while it has been shown by the examples herein that certain specifiedamounts of hydrogen cyanamide, or of hydrogen cyanamide and ureatogether, provide outstanding antifreeze properties in the gelcompositions, it will be appreciated that the amounts of these materialsused may be varied over a wider range than encompassed by the exampleswith significant anti-freeze benefits still being attained. Thus,expressed on a dry basis (as distinguished from the hydrogen cyanamidesolution used to supply it) at least about 1% and preferably about 2% ofhydrogen cyanamide is required for sub-Zero anti-freeze protection.However, as little as 0.5% will provide significant improvement and evenfull protection at temperatures upwards of about 0 F. Also, higheramounts than designated in the examples may be used without substantialdetraction from the benefits of the invention. In general, therefore,the amount of hydrogen cyanamide to be used in the gel compositions canrange from about 0.5 to about 10% with the preferred amounts being fromabout 1% to about 2%. For the sake of clarity, it is pointed out thepercentages of hydrogen cyanamide recited in the following claims arealso expressed on a dry basis.

With respect to urea, the amount which may be used in conjunction withthe hydrogen cyanamide can range from about 1% to about 10% with thepreferred amount being from about 1% to about 3 Having now fullydescribed the invention, what is claimed as new and patentable is:

1. An explosive gel composition of improved antifreeze propertiescomprising on a weight basis (a) from about 15-50% of ammonium nitrate,(b) from about 5-25% of sodium nitrate, (c) from about 5-40% of asensitizer, (d) from about 0.5-2% of a gelling agent, (e) from about5-25% of water, (f) from about 05-10% of hydrogen cyanamide and (g) from0-10% urea.

2. An explosive gel composition according to claim 1 wherein thesensitizer is trinitrotoluene.

3. An explosive composition according to wherein the sensitizer is fueloil.

4. An explosive composition according to wherein the sensitizer isaluminum.

5. An explosive composition according to wherein the gelling agent isguar gum.

6. An explosive composition according to claim 1 wherein the gellingagent is a high molecular weight polyacrylamide.

7. An explosive gel composition according to claim claim 1 claim 1 claim1 1 wherein the urea is present in an amount of from about 1% to about3%.

8. An explosive gel composition of claim 6 wherein the hydrogencyanamide is present in an amount of from about 1% to about 2% and ureais present in an amount of from about 1 to about 3%.

9. An explosive composition according to claim 1 wherein the sensitizeris comprised of trinitrotoluene and aluminum.

References Cited UNITED STATES PATENTS 3,004,842 10/ 1961 Rowlinson149-43 X 3,052,578 9/1962 Davis et a1 149-600 3,190,777 6/1965 Breza etal 149--46 X 3,238,074 3/1966 Griflith et al. l49-44 X 3,249,476 5/1966Clay et al. 149-39 X 3,296,042 1/ 1967 Quadfiieg et a1 149-60 X CARL D.QUARFORTH, Primary Examiner.

S. J. LECHERT, JR., Assistant Examiner.

